Mitotic Rate and Your Melanoma Pathology Report

Mitotic rate measures how quickly cancer cells are dividing and growing. The mitotic rate listed on your cancer pathology report helps your healthcare provider better understand your melanoma diagnosis and develop a treatment strategy.

This article explains mitotic rate, what it means, and why it's important.

Doctor examining woman's skin
 

What Mitotic Rate Means

Mitotic rate (MR) describes how fast cancer cells are dividing and growing. It is listed on your pathology report along with information including:

  • Tumor stage, how advanced the cancer is and whether it has spread
  • Clark level, how deeply the tumor has grown into the skin, and which skin layers are involved
  • Breslow thickness, how thick the tumor is
  • Ulceration, when melanoma breaks through the overlying skin

The pathology report is prepared by a pathologist, a practitioner who examines tissues and fluids to diagnose disease.

If you have a suspicious lesion or mole, your healthcare provider will send a biopsy specimen to the pathologist. The pathologist will examine the sample under a microscope. If malignant (cancerous) cells are found, your healthcare provider may order other tests to determine its stage and find out whether it has spread.

To measure MR, the pathologist examines the surgically removed tumor with a microscope and manually counts the number of cells exhibiting mitosis. Mitosis is an easily identifiable characteristic of dividing cells. The measurement is given as the number of mitoses per square millimeter.

The higher the mitotic count, the more likely the tumor is to have metastasized (spread). This is because rapidly dividing cells are more likely to invade the blood or lymphatic vessels and thus spread around the body.

Research has shown that the odds of survival for patients with melanoma are better for people with a lower mitotic rate. For example, people with a mitotic rate of 0 mitoses per square mm have an average five-year overall survival rate of 97.3%, while those with a mitotic rate of 4 to 10 mitoses per square mm have an average five-year overall survival rate of 73%. A higher MR is also associated with an increased risk of recurrence.

Additionally, the mitotic rate can help predict if your sentinel lymph node biopsy will be positive or not. A sentinel lymph node is the first lymph node where cancer is most likely to spread.

How Important Is Mitotic Rate in Melanoma?

Many studies have confirmed that the mitotic rate is a significant predictor of outcomes in patients with melanoma, although some controversy still exists. Two issues are under debate:

  • Is MR independent of other prognostic factors?
  • If not, is measuring MR worth the time and expense?

Although MR has no role in the current staging system for melanoma, research has demonstrated that it is a more important prognostic factor than ulceration, which does have an important role in staging.

Some healthcare providers, however, believe that the mitotic rate is not an independent prognostic factor because it is closely related to tumor (Breslow) thickness and ulceration.

For example, the American Academy of Dermatology's current guidelines recommend including mitotic rate on the pathology report. Other experts argue that measuring the MR should only be done in large academic (university) medical centers for future research purposes.

If the MR isn't included in your pathology report, ask your healthcare provider about their reasoning for excluding it.

Talking With Your Healthcare Provider

Always request a copy of your pathology report. Read it and ask your healthcare provider questions about it. Don't hesitate to get a second opinion about the diagnosis from a specialist, such as a dermatopathologist.

A knowledgeable patient is an empowered patient and one who can make better treatment choices that lead to better outcomes.

Summary

In melanoma, mitotic rate is a measurement of how quickly cancer cells are dividing and growing. It appears on your pathology report along with other measurements like Breslow thickness and ulceration.

Mitotic rate is not currently used to determine cancer staging, but it can help your healthcare team judge potential outcomes and develop a treatment strategy.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Melanoma Research Alliance. Breslow depth and Clark level Breslow depth.

  2. AIM at Melanoma Foundation. Understanding your pathology report.

  3. Ghasemi Basir HR, Alirezaei P, Ahovan S, Moradi A. The relationship between mitotic rate and depth of invasion in biopsies of malignant melanoma. Clin Cosmet Investig Dermatol. 2018;11:125-130. doi:10.2147/CCID.S158043

  4. Patuzzo R, Mattavelli I, Gallino G, et al. The prognostic role of mitotic rate in cutaneous malignant melanoma: Evidence from a multicenter study on behalf of the Italian Melanoma Intergroup. Cancer. 2023;129(15):2331-2340. doi:10.1002/cncr.34824

  5. von Schuckmann LA, Hughes MCB, Ghiasvand R, et al. Risk of melanoma recurrence after diagnosis of a high-risk primary tumor. JAMA Dermatol. 2019;155(6):688-693. doi:10.1001/jamadermatol.2019.0440

  6. Ly CL, Blaha O, Wei W, et al. Predictive accuracy of elevated mitotic rate on lymph node positivity and recurrence in thin melanomas. Front Oncol. 2023;12:1077226. doi:10.3389/fonc.2022.1077226

  7. Wan G, Nguyen N, Liu F, et al. Prediction of early-stage melanoma recurrence using clinical and histopathologic features. NPJ Precis Oncol. 2022;6(1):79. doi:10.1038/s41698-022-00321-4

  8. Tas F, Erturk K. Ulceration vs. mitosis in cutaneous melanoma: Which is superior for predicting prognosis across clinical stages? Cancer Invest. 2022;40(10):842-851. doi:10.1080/07357907.2022.2133139

  9. Swetter SM, Tsao H, Bichakjian CK, et al. Guidelines of care for the management of primary cutaneous melanoma. J Am Acad Dermatol. 2019;80(1):208-250. doi:10.1016/j.jaad.2018.08.055

Additional Reading
  • Melanoma. National Comprehensive Cancer Network. V1.2009.
  • Attis MG, Vollmer RT. Mitotic rate in melanoma: a reexamination. Am J Clin Pathol. 2007;127(3):380-4. DOI: 10.1309/LB7RTC61B7LC6HJ6

  • Barnhill RL, Katzen J, Spatz A, Fine J, Berwick M. The importance of mitotic rate as a prognostic factor for localized cutaneous melanoma. J Cutan Pathol. 2005;32(4):268-73. DOI: 10.1111/j.0303-6987.2005.00310.x

  • Understanding a Cancer Diagnosis: Skin Melanoma. College of American Pathologists. 

By Timothy DiChiara, PhD
Timothy J. DiChiara, PhD, is a former research scientist and published writer specializing in oncology.